Examples of known fuel injector use an armature assembly having an armature that reciprocates between an open position and a closed position. The distance that the armature travels is known as an injector lift height, working air gap or distance. The working air gap or distance is one of many variables that determine the amount of fuel that will be dispensed outside the fuel injector when the injector is actuated.
The air gap is believed to be set by first taking a series of direct contact measurements. One direct measurement is believed to determine the distance between a contact face of a pole piece of the armature assembly and a sealing diameter of a seat. Another direct measurement is believed to determine the distance between the sealing diameter of a seat and the position of a closure member during a full open position. The difference between these two measurements determines the approximate working gap. The actual working gap is believed to be set by using a deformable ring that is inserted into a shoulder formed at one end of a valve body. The ring is subsequently crushed to the approximate working gap.
The actual working gap, however, may vary between individual injectors due to variations in the direct measurement operations, the deformability of the crush ring material or the valve body. Moreover, the direct measurements oftentimes can introduce contaminants into the fuel injector, leading to the possibility of inconsistent injector performance. Additionally, the crushing operation is believed to introduce undesirable structural loading on the body of the injector. Furthermore, the use of crush ring is believed to require random samplings of the crush ring and injectors to maintain consistent injector performance. Finally, once the crush ring is installed or crushed, it is believed that no adjustment can be made unless the crush ring is extracted and replaced with a new one.
Referring to FIG. 1, an enlarged partial view of a fuel injector extending between axis Axe2x80x94A, having a housing or valve body 200, an armature assembly 210 and a ferromagnetic coil 220 disposed between inlet end 300A and outlet end 300B. The armature assembly 210 can include an armature 212, armature tube 216 and a closure element 218. The armature tube 216 can be integrated with the armature 212 for a two-piece armature assembly. Alternatively, the armature tube 216 can be integrated with the closure 218. The armature assembly 210 is magnetically coupled to an electromagnetic actuator assembly that includes a pole piece or a stator 214, coil 220 and bobbin. The valve body 200 is affixed to a shell 350 that is further affixed to the pole piece 214. An elastic member 225 that can be a coil spring is disposed between the movable armature 214 and the fixed stator 214. The elastic member 225 operates to bias the armature assembly 210 towards the outlet end 300B of the injector, thereby forming a gap xcex94 between the stator 214 and the armature 212. Although disclosed as a single spring, the elastic member 225 can include more than one coil spring for a multi-spring rate elastic member. A flow metering device or seat 244 at the outlet end 300B of the injector engages the armature assembly 210, and prevents the elastic member 225 from pushing the armature assembly 210 out of the valve body 200. Where the seat 244 is located defines how far the elastic member 225 can separate the armature assembly 210 from the stator 214. In other words, the elastic member 225 and seat 244 cooperate to define a working gap xcex94 between the armature 212 and the stator 214. Finally, the location of the seat 244 also sets a spring preload on elastic member 225 that acts on the armature assembly 210 by the elastic member 225.
The present invention further provides a method of setting a working gap of an armature assembly in a fuel injector. The fuel injector includes a housing including a first end and a second end extending between a longitudinal axis, a housing having a flow passage extending between the first and second ends, an electromagnetic actuator including a stator and an armature assembly, a spring disposed between the stator and the armature assembly and operable to push the armature assembly towards the second end to form a gap therein. The method comprises inserting a sleeve and a flow metering assembly within the flow passage, the flow metering assembly limiting the movement of the armature assembly towards the second end, and limiting the inserting of the flow metering assembly along the longitudinal axis toward a first end by a position of the sleeve, the position defining the magnitude of the gap between the stator and the armature assembly.